Electrode Mixture Manufacturing Method And Electrode Mixture

ABSTRACT

The present invention provides: an electrode mixture manufacturing method comprising the processes of introducing a first binder, an electrode active material, and a conductive material into an extruder, performing a first mixing of the first binder, the electrode active material, and the conductive material in the extruder, additionally introducing a second binder into the extruder and performing a second mixing, and yielding an electrode mixture resulting from the first mixing and the second mixing; an electrode mixture manufactured thereby; and an electrode manufacturing method using the electrode mixture.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No.16/604,801, filed on Oct. 11, 2019, which is a national phase entryunder 35 U.S.C. § 371 of International Application No.PCT/KR2018/011435, filed on Sep. 27, 2018, which claims priority fromKorean Patent Application No. 10-2017-0128263, filed on Sep. 29, 2017,the disclosures of which are incorporated herein by reference in theirentirety.

TECHNICAL FIELD

The present invention relates to a method for manufacturing an electrodemixture and a method for forming an electrode mixture.

Background Art

Lithium secondary batteries have been used not only as energy sourcesfor mobile devices but also as power sources for electric vehicles (EVs)and hybrid electric vehicles (HEVs) in recent years. In addition, theyare also used as assist power sources by using grids.

The manufacturing process of such a lithium secondary battery is roughlyclassified into an electrode process, an assembly process, and anactivation process. The electrode process may be divided into an activematerial mixing process, an electrode coating process, a drying process,a rolling process, a slitting process, and a winding process.

Among them, the active material mixing process is a process of mixing acoating material for forming an electrode active layer in which anactual electrochemical reaction takes place at an electrode.Specifically, the active material mixing process is to a process ofmanufacturing in the form of a slurry having fluidity by mixing anelectrode active material, which is an essential element of theelectrode, with a conductive material and filler which are otheradditives, a binder for adhesion between particles and adhesion of acurrent collector, and a solvent for imparting viscosity and dispersingparticles.

The composition thus mixed for forming the electrode active layer may bereferred to as an electrode mixture in a broad sense.

Thereafter, an electrode coating process for applying the electrodemixture onto the electrically conductive current collector and a dryingprocess for removing the solvent contained in the electrode mixture areperformed, and the electrode is further rolled to a predeterminedthickness.

On the other hand, as the solvent contained in the electrode mixture isevaporated during the drying process, defects such as pinholes andcracks may be induced in the pre-formed electrode active layer.

In addition, since the inside and the outside of the active layer arenot uniformly dried, there may be a gap with the relatively later driedportion as the particles at the earlier dried portion float, i.e., dueto the particles floating according to the difference in the solventevaporation rate, thereby deteriorating the quality of the electrode.

In order to solve the above problems, a drying device capable ofcontrolling the evaporation rate of the solvent while allowing theinside and outside of the active layer to be uniformly dried has beenconsidered, but these drying devices are very expensive and requireconsiderable cost and time for operation, and have poor manufacturingprocessability.

Therefore, there is a high need for a technology capable of improvingthe manufacturing processability of the electrode.

DISCLOSURE Technical Problem

It is an object of the present invention to solve the above-mentionedproblems of the prior art and the technical problems required from thepast.

Specifically, an object of the present invention is to provide anelectrode mixture which does not contain a solvent and which does notrequire a separate drying process. Another object of the presentinvention is to provide a method for manufacturing an electrode mixturewithout a solvent.

Technical Solution

In order to achieve the above object, the present invention provides amethod of manufacturing an electrode mixture for a secondary battery.

Specifically, it is a method for manufacturing an electrode mixture fora secondary battery, the method including:

a process of injecting a first binder, an electrode active material anda conductive material into an extruder;

a first mixing process of mixing the first binder, the electrode activematerial and the conductive material in the extruder;

a second mixing process of further adding a second binder to theextruder; and

a process of obtaining an electrode mixture derived from the firstmixing process and the second mixing process;

That is, the method according to the present invention is a method inwhich the first binder and the second binder are charged stepwise, andthe binding of the electrode active material and the conductivematerials, which are components of the mixture, is stepwise induced, tothereby achieve adhesion to each other in a dispersed state.

In addition, since the electrode material mixture is prepared withoutusing a solvent, it is possible to realize a mixture having littlefluidity, and in the case of such an electrode material mixture, it iseasy to handle and can be processed in desired forms to be used inmanufacturing various forms of electrodes.

In addition, if the electrode mixture prepared by the method of thepresent invention is used in the production of electrodes, the dryingprocess for removing the solvent can be omitted, so that the method ofthe present invention can solve the fundamental problem about improvingthe manufacturability of the electrode.

In one specific example, in the first mixing process, first particleswhich are electrode active materials, second particles which areconductive materials, and granular first powders which are generated asthe first particles and/or the second particles are attached to thefirst binder are produced.

In the second mixing process, the second binder may be fiberized to forma network physically connecting the first powders.

In other words, the first powder and the second particles are combinedto constitute the first powder, and the first powders dispersed in thefirst mixing process are coupled to or connected to the network duringthe second mixing process, from which it can be seen that each particleexists in a sufficiently dispersed state. As a result, it is possible toform a lump-shaped electrode mixture having a solid content of 100%.

In addition, one of the characteristics of the present invention is toproduce an electrode material mixture using an extruder, and inparticular, a shearing stress due to the extruder is formed in a secondbinder so that a plurality of short fibers can form a network, and atthis time, the short fibers may be connected to the first binder,directly to the first powder, or to both the first binder and the firstpowder.

Thus, since the method of the present invention causes a network fromthe second binder and allows the first powders to be congealed, one lumpis formed without a solvent, so it is possible to manufacture anelectrode mixture of 100% solids, and the electrode mixture can beeasily handled and processed as explained above.

In summary, the method according to the present invention is completelydifferent from the conventional technology using a solvent. Instead ofusing a dispersion and a viscosity imparting scheme using a solvent, thealready dispersed first powder is connected using a network formed byfiberization of the second binder and an electrode mixture having almostno fluidity is manufactured.

In one specific example, the second binder may bepolytetrafluoroethylene (PTFE), and the first binder may be one or moreselected from polyethylene oxide (PVDF), polyvinylidene fluoride (PVdF),and polyvinylidene fluoride-co-hexafluoropropylene (PVdF-HFP).

The content of the second binder may be between 0.8% and 1%, and morespecifically between 0.9% and 1%, based on the total weight of themixture bulk.

The content of the first binder may be between 2.1% and 2.4%, and morespecifically be 2.1% or 2.4%, based on the total weight of the mixturebulk.

In one specific example, the electrode active material may be a positiveelectrode active material. Herein, in the first and second mixing andkneading processes, the extruder may be operated at a temperature of 20to 60 degrees Celsius, at 30 rpm to 70 rpm with the maximum torque of180 NM. At this time, PVdF-HFP (polyvinylidenefluoride-co-hexafluoropropylene) may be used as the first binder, andpolytetrafluoroethylene (PTFE) may be used as the second binder.

In the case of a positive electrode, the content of the first binder maybe between 2.1% and 2.2%, more specifically be 2.1% of the total weightof the mixture bulk.

In addition, the content of the second binder in the positive electrodemay be between 0.8% and 1%, and more specifically be 0.9% of the totalweight of the mixture bulk.

If the content of the binders is out of the range, in the extruder, theextruder may be stopped with excessive fiberification of the binders.

When the content of the second binder is less than 0.8%, sincesufficient fiberization is not performed, cohesiveness to maintain theshape of the mixture bulk is not present, and if the content exceeds 1%,excessive fiberization of the second binder causes the over torque,thereby making it difficult to obtain a mixture bulk.

The positive electrode active material may be a layered compound such aslithium cobalt oxide (LiCoO₂), lithium nickel oxide (LiNiO₂), or acompound substituted with one or more transition metals; lithiummanganese oxides such as Li_(1+x)Mn_(2−x)O₄ (herein, x is between 0 and33), LiMnO₃, LiMn₂O₃, and LiMnO₂; lithium copper oxide (Li₂CuO₂);vanadium oxides such as LiV₃O₈, LiFe₃O₄, V₂O₅, and Cu₂V₂O₇; Lithiumnickel oxide expressed by LiNi_(1−x)M_(x)O₂ (herein, M=Co, Mn, Al, Cu,Fe, Mg, B or Ga, and x=0.01 to 0.3); and a lithium manganese compoundoxide expressed by LiMn_(2−x)M_(x)O₂ (where M=Co, Ni, Fe, Cr, Zn or Ta,and x=0.01 to 0.1) or Li₂Mn₃MO₈ (where M=Fe, Co, Ni, Cu or Zn); LiMn₂O₄in which a part of Li is substituted with an alkaline earth metal ion;disulfide compounds; Fe₂(MoO₄)₃, etc., but not limited thereto.

The electrode active material may also be a negative electrode activematerial. Herein, in the first and second mixing and kneading processes,the extruder may be operated at a temperature of 80 to 120 degreesCelsius, at 30 rpm to 70 rpm with the maximum torque of 80 NM.

In the preparation of the negative electrode, a PVdF-HFP (polyvinylidenefluoride-co-hexafluoropropylene) alone may be used as the first binder,or in some cases, a mixture of polyethylene oxide (PVDF) andpolyvinylidene fluoride-co-hexafluoropropylene (PVdF-HFP) may be used asthe first binder.

Here, PEO and PVdF-HFP can be mixed in a ratio of 1:9 to 9:1,specifically 2:8 to 8:2, more specifically 4:6 to 6:4.

The second binder may be polytetrafluoroethylene (PTFE) alone.

In the case of a negative electrode, the irreversibility due to thefibrous second binder may be increased, so the content of the secondbinder should be particularly carefully checked.

Accordingly, in the present invention, the content of the second bindermay be between 0.9% and 1%, and more specifically be 1% of the totalweight of the mixture bulk.

The content of the first binder may be between 2.3% and 2.4%, and morespecifically be 2.4% of the total weight of the mixture bulk.

Examples of the negative electrode active material include carbon suchas non-graphitized carbon and graphite carbon; metal complex oxide suchas Li_(x)Fe₂O₃(0≤x≤1), Li_(x)WO₂(0≤x≤1), Sn_(x)Me_(1−x)Me′_(y)O_(z) (Me:Mn, Fe, Pb, Ge; Me′: Al, B, P, Si, groups 1, 2, and 3 of the periodictable, halogen; 0<x≤1; 1≤y≤3; 1≤z≤8); lithium alloy; silicon alloy; tinalloy; metal oxides such as SnO, SnO₂, PbO, PbO₂, Pb₂O₃, Pb₃O₄, Sb₂O₃,Sb₂O₄, Sb₂O₅, GeO, GeO₂, Bi₂O₃, Bi₂O₄, and Bi₂O₅; conductive polymerssuch as polyacetylene; and Li-Co-Ni-based materials.

The conductive material may typically be added in an amount of 1 to 30wt % based on the total weight of the mixture. Such a conductivematerial is not particularly limited as long as it has electricalconductivity without causing a chemical change in the battery, andexamples thereof include graphite such as natural graphite andartificial graphite; carbon black such as carbon black, acetylene black,Ketjen black, channel black, furnace black, lamp black, and summerblack; conductive fibers such as carbon fiber and metal fiber; metalpowders such as carbon fluoride, aluminum and nickel powder; conductivewhiskey such as zinc oxide and potassium titanate; conductive metaloxides such as titanium oxide; and conductive materials such aspolyphenylene derivatives and the like.

In some cases, a filler, which is a component for suppressing theexpansion of the electrode, may be further added in the first mixingprocess or the second mixing process. The filler is not particularlylimited as long as it is a fibrous material without causing a chemicalchange in the battery, and examples thereof include olefin polymers suchas polyethylene and polypropylene; and fibrous materials such as glassfibers and carbon fibers.

The processing of the above-mentioned form means, for example, that theobtained electrode mixture is transformed into a desired shape such as awound shape, a wave shape, a film shape, etc. In one example thereof, aprocess of rolling a mixture, obtained through the above process, in afilm form having an average thickness of 1 micrometer to 100 micrometersmay be further included.

In order to achieve the above object, the present invention alsoprovides an electrode material for forming an electrode for a secondarybattery.

The electrode mixture includes a first binder, a second binder, anelectrode active material, and a conductive material,

The first binder forms a first powder by bonding first particles as anelectrode active material, second particles as a conductive material andthe first particles and/or second particles,

The second binder forms a network in a form of short fibers, and thefirst powders are physically connected to the network.

Namely, since the electrode mixture according to the present inventiondoes not contain a solvent, it is easy to handle due to its lowfluidity, and can be processed into a desired shape and used in varioustypes of electrodes. In addition, if the electrode mixture of thepresent invention is used in the production of an electrode, the dryingprocess for removing the solvent can be omitted, thereby significantlyimproving the processability of the manufacturing of the electrode.

In the electrode mixture, the first powders connected to the network mayform an integral body, and the integral body may be in the form of anirregular lump or a film rolled with a regular thickness.

This is because the network derived from the second binder is entangledwith the first powders so that the form of one lump can be maintainedand, on the basis thereof, it can be processed in the form of a film.

In one specific example, the second binder may bepolytetrafluoroethylene (PTFE).

In one specific example, the first binder may be one or more selectedfrom the group consisting of polyethylene oxide (PVDF), polyvinylidenefluoride (PVdF) and polyvinylidene fluoride-co-hexafluoropropylene(PVdF-HFP), and more specifically a mixture of polyethylene oxide (PEO)and PVdF-HFP (polyvinylidene fluoride-co-hexafluoropropylene), orPVdF-HFP alone.

Here, PEO and PVdF-HFP can be mixed in a ratio of 1:9 to 9:1,specifically 2:8 to 8:2, more specifically 4:6 to 6:4.

The content of the second binder may be between 0.8% and 1%, and morespecifically between 0.9% and 1%, based on the total weight of themixture bulk.

The content of the first binder may be between 2.1% and 2.4%, and morespecifically be 2.1% or 2.4%, based on the total weight of the mixturebulk.

If the content of the binders is out of the range, in the extruder, theextruder may be stopped with excessive fiberification of the binders.

When the content of the second binder is less than 0.8%, sincesufficient fiberization is not performed, cohesiveness to maintain theshape of the mixture bulk is not present, and if the content exceeds 1%,excessive fiberization of the second binder causes the over torque,thereby making it difficult to obtain a mixture bulk.

The electrode active material may be a positive electrode activematerial or a negative electrode active material, and examples of theelectrode active material may be those described in the above.Similarly, the materials described in the above can also be used as theconductive material.

The present invention also provides a method of manufacturing anelectrode including the electrode mixture.

The method specifically includes: a process in which an electrodemixture in the form of a film is placed on a conductive metal currentcollector; and

a process of applying heat and pressure to the electrode mixture or themetal current collector to laminate each other.

Herein, the process of lamination may include rolling the attachedelectrode mixture to a predetermined thickness.

The current collector is not particularly limited as long as it has highconductivity without causing a chemical change in the battery. Forexample, the current collector may be made of a metal such as stainlesssteel, aluminum, nickel, titanium, sintered carbon, cooper, or aluminumor stainless steel of which the surface is treated with carbon, nickel,titanium, or silver, or the like. The current collector may have fineirregularities on the surface thereof to increase the adhesion of thepositive electrode active material, and various forms such as a film, asheet, a foil, a net, a porous body, a foam, and a nonwoven fabric arepossible.

As described above, in the electrode mixture according to the presentinvention and the method of manufacturing an electrode using the same,the drying process can be omitted, thereby significantly improving themanufacturing processability.

Advantageous Effects

As described above, the method for manufacturing an electrode mixtureaccording to the present invention is characterized in that a network isformed by fiberization of a second binder instead of a solvent, so it iseasy to handle and be processed into a desired shape to thereby be usedin manufacturing various forms of electrodes.

In addition, since the electrode mixture according to the presentinvention does not contain a solvent, it is easy to handle due to itslow fluidity, and can be processed into a desired shape and used invarious types of electrodes. In addition, if the electrode mixture ofthe present invention is used in the production of an electrode, thedrying process for removing the solvent can be omitted, therebysignificantly improving the processability of the manufacturing of theelectrode.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an actual photograph of an electrode mixture prepared inExample 1.

FIG. 2 is an actual photograph of the electrode mixture prepared inComparative Example 1.

FIG. 3 is a photograph of the electrode mixture of Example 1 observedwith a scanning electron microscope.

FIG. 4 is a photograph of the electrode mixture of Example 2 observedwith a scanning electron microscope.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, the present invention will be described with reference toembodiments thereof, but it should be understood that the scope of thepresent invention is not limited thereto.

EXAMPLE 1

Among the total weight of the electrode mixture, 94% by weight of alithium-transition metal composite oxide including nickel, manganese andcobalt, 3% by weight of Denka black and 2.1% by weight of PVDF-HFP werecharged into a Rheomix 300™ extruder of Thermo. Then the mixing isperformed at 40 degrees C. for about 5 minutes at a maximum torque of180 NM and 50 rpm. Then PTFE corresponding to 0.9% by weight among thetotal weight of the already injected materials was added and the mixturewas further mixed for about 10 minutes to obtain an electrode mix.

EXAMPLE 2

Among the total weight of the electrode mixture, 95.6% by weight ofgraphite, 1% by weight of Denka black and 2.4% by weight of PVDF-HFPwere charged into a Thermo Rheomix 300™ extruder. Then the mixing wasperformed at 100 degrees C. at a maximum torque of 80 NM and 50 rpm.Then PTFE corresponding to 1% by weight among the total weight ofalready injected materials was added and the mixture was further mixedfor about 10 minutes to obtain an electrode mixture.

COMPARATIVE EXAMPLE 1

An electrode mixture was prepared in the same manner as in Example 1,except that 2.5% by weight of PVDF-HFP and 0.5% of PTFE were added.

EXPERIMENTAL EXAMPLE 1

The shapes of the electrode assemblies prepared in Example 1 andComparative Example 1 were visually compared, and the resultingphotographs are shown in FIGS. 1 and 2 , respectively.

In the case of FIG. 1 , which is a result of Example 1, it can be seenthat the electrode mixture is obtained in the form of a lump in whichthe electrode mixture is fully aggregated.

In the case of FIG. 2 , which is a result of Comparative Example 1, itcan be seen that the electrode mixture is incomplete and notagglomerated. This is presumably due to the fact that due to therelatively small amount of the second binder, fibrosis to bind theelectrode active materials is not sufficiently formed, and therefore thecohesive force is not inherent enough to form a certain shape of theelectrode mixture.

EXPERIMENTAL EXAMPLE 2

The electrode mixture obtained in Example 1 was observed through ascanning electron microscope and the result is shown in FIG. 3 .

Referring to FIG. 3 , in the case of the electrode mixture obtained inthe examples, it can be confirmed that the fibrous PTFE forms thenetwork (circle) and binds the powders.

EXPERIMENTAL EXAMPLE 3

The electrode mixture obtained in Example 2 was observed through ascanning electron microscope and the result is shown in FIG. 4 .

Referring to FIG. 3 , in the case of the electrode mixture obtained inthe examples, it can be confirmed that the fibrous PTFE forms thenetwork and binds the powders.

While the present invention has been described with reference toexamples, it is to be understood that the invention is not limited tothe examples, but is intended to cover various modifications andequivalent arrangements included within the spirit and scope of theappended claims.

1. An electrode mixture forming an electrode for a secondary battery,the electrode mixture comprising: a first binder, a second binder, anelectrode active material, and a conductive material, wherein the firstbinder forms a first powder by bonding first particles as an electrodeactive material, second particles as a conductive material and the firstparticles and/or second particles, and wherein the second binder forms anetwork in a form of short fibers, and the first powders are physicallyconnected to the network.
 2. The electrode mixture of claim 1, whereinthe first powders connected to the network forms an integral body, andthe integral body is in the form of an irregular lump or a film rolledwith a regular thickness.
 3. The electrode mixture of claim 1, whereinthe second binder is polytetrafluoroethylene (PTFE).
 4. The electrodemixture of claim 1, wherein the first binder is one or more selectedfrom the group consisting of polyethylene oxide (PEO), polyvinylidenefluoride (PVdF), and polyvinylidene fluoride-co-hexafluoropropylene(PVDF-HFP).
 5. The electrode mixture of claim 1, wherein the content ofthe first binder is 2.1% to 2.4% based on the total weight of theelectrode mixture, and wherein the content of the second binder is 0.8%to 1% based on the total weight of the electrode mixture.
 6. A method ofmanufacturing an electrode comprising any one of the electrode mixturesof claim 1, the method comprising: a process in which an electrodemixture in the form of a film is placed on a conductive metal currentcollector; and a process of applying heat and pressure to the electrodemixture or the metal current collector to laminate each other.
 7. Themethod of claim 6, wherein the process of lamination further comprisesrolling the attached electrode mixture to a predetermined thickness.